In Reply: We accept that seasonal variation in temperature and rate of respiratory tract infection may have had an effect on our study data, but believe that any contribution from these factors would have been minor and would not explain the magnitude of changes that were observed. Data from Health Protection Scotland for 2005/20061 (perhaps a better indicator of the potential influence of concomitant respiratory illness on our data than a 10-patient study in Finland2) show that the general practitioner consultation rate in Scotland for acute respiratory tract illness in adults aged 20 to 49 years was greater in the week during which the final data were gathered compared with the last week in February when the baseline measurements were made. It is therefore more likely that the observed decrease in white blood cell count (which was commensurate with the decrease in serum cotinine) is explained by reduced exposure to secondhand smoke. Notably, the magnitude of change in total white blood cell count after the introduction of the ban compared with preban levels was comparable with previous data that showed exposure to secondhand smoke causes an increase in this inflammatory index.3